Stabilized ice-cream mixes



Patented Oct. 25, 1949 2,485,935 STABILIZED ICE-CREAM MIXES Arnold B.Steiner, La Jolla, and Gerald D. Sperry, San Diego, Calii'., assignorsto Kelco Company, San Diego, Calif., a corporation of Delaware NoDrawing. Application September 16, 1947, Serial No. 774,424

4 Claims. (Ci. 99-136) This invention relates to improvements in themanufacture of ice cream and other frozen milk products and specificallyto the stabilization of such products against ice crystal growth and tothe production of a smooth and creamy body.

An ice cream mix consists essentially of a mixture of creams, milks andsugars so proportioned as to contain desired percentages of sugar,butter fat and milk solids. These proportions vary with traderequirements but may be said to average about 12% butter fat, 10% serumsolids and 16% sugar by weight.

To produce an ice cream having a smooth body and to prevent the growthof ice crystals in storage it is common practice to add a smallproportion of a stabilizer such as a sodium alginate composition. Sodiumalginate alone is not adapted to this use, by reason of itsincompatibility with the calcium salts of the milk and the dimculty inbringing it into solution in the mix, and it is therefore commonly usedin the form of a composition.

This composition, described in United States Patent 2,097,228 to HowardJ. Lucas, ordinarily contains about one-half part by weight of sodiumalginate, the remainder being sugar and/or dextrin to assist indispersing the .solid alginate through the mix and thus promoting itssolution, together with a buffer salt such as a water-soluble salt ofphosphoric acid which functions to prevent precipitation of the alginicsalt by calcium salts. In this composition an alginic salt, sodiumalginate, is the effective stabilizing agent and the composition isreferred to hereinafter as alginic salt composition to distinguish itclearly from the alginic esters which are the subject of the presentinvention.

While this alginic salt composition is a highly efiective stabilizer forice cream it has certain undesirable inherent properties which limit itscommercial usefulness. These undesirable properties are not such asreduce the stabilizing value of the composition but have regard tocertain elements of inconvenience in use and interference with thesmooth progress of the mix through the succession of steps ofmanufacture of the frozen product. These undesirable characteristics ofthe composition are as follows:

' (a) The relatively high temperature required to bring the alginic saltcomponent into solution in the mix;

(b) The slow and viscid flow of the mix over the cooler and theattendant lowering of the cooling rate;

The incompatibility of the composition with mixes having a developedacidity.

As described in detail in connection with the experiments following, thedrawbacks incident to the use of the alginic salt composition are wholly-in such mixes without buffering.

avoided in the use as a stabilizer of the propylene glycol ester ofalginic acid.

This ester may be prepared by the methods described in U. S. Patent2,426,125 to Arnold B. Steiner and in the copending application ofArnold B. Steiner and William H. McNeely, filed December 22, 1945, underSerial No. 636,938. These methods consist, briefly, in reacting alginicacid with an excess of propylene oxide, with or without a previouspartial neutralization of the acid with an alkali metal or ammonia. Thereaction product, propylene glycol alginate (hereinafter referred to asthe alginic ester), dissolves in water to give a pH value ordinarilybelow 5.0 and shows reduced reactivity with the salts and the acidswhich gelatinize or precipitate the soluble alginic salts.

While the alginic ester is more nearly compatible with calcium saltsthan are the soluble salts of alginic acid, this compatibility decreasesas the pH of the solution is increased. For example, at pH 3.5 asolution of the alginic ester gives a soft gel when mixed with a calciumchloride solution; at pH 4.2 a harder gel is formed, and at pH 6.0 thesolution rapidly sets up as a firm gel of still harder consistency.Prolonged heating to the boiling point does not melt this gel nor causeit to dissolve.

As the calcium salt content of ice cream mixes is highly appreciable(varying from 0.1 to 0.3% of the weight of milk present) and as the pHvalue of the mix ranges from 6.1 to 6.4, it is surprising to find thatthe alginic ester is soluble In many or most instances the alginic esterper se is more readily soluble than the buffered alginic saltcomposition, and no addition of phosphate or other buffer salts isrequired.

Again, solutions of the alginic ester are known to vary widely inviscosity, at equal concentrations, with change in pH value and to havevery low viscosities as the neutral point is approached. For example, a1 4% solution of propylene glycol alginate having a viscosity of 1000centipoises at pH 3.5 decreased rapidly in viscosity as the pH value wasgradually increased and had a viscosity of only centipoises at pH 6.0.As the stabilizing value of sodium alginate falls off rapidly as theviscosity producing factor of the alginate decreases, and as the pHvalue of an ice cream mix is in the range in which the viscosity of thealginic ester is very low, it was expected that the unit stabilizingvalue of the ester would be correspondingly low, that is, that thequantity required to produce satisfactory stabilization would be large.The fact proved to be to the contrary. the alginic ester of lowviscosity being fully as effective in stabilization of ice cream as analginic salt composition of higher viscosity, no greater percentageaddition to the mix being required. The actual utility of propyleneglycol alginate as an ice cream stabilizing agent is best shown byComparing its various features of behavior with those of the alginicsalt composition, this SOLUTION TEIVIPERATURE Solution of the alginicsalt composition in the mix is slow and imperfect if the temperature beless than about 160 Fahr. at the time of addition. At lowertemperatures, even with extended time, the composition is insoluble andno benefit is obtained from its use. For example, if the composition beadded to the cold mix (e. g., at 60 F.)

which is then brought up to temperature and pasteurized for one-halfhour at 160 F. or even at the boiling point, 212 F., the compositionforms clumps and fails to dissolve. About the lowest temperature atwhich it may be added is 145 F. and at that temperature solution isimperfect. On the other hand, the alginic ester dissolves readily at 110Fahr. whether added at that temperature or to the cold mix. This factoris of major importance where it is preferred to pasteurize at lowtemperatures, of the order of 145 F. Also it is very convenient for theice cream manufacturer to be able to add all of the dry ingredients(sugar, milk powder and stabilizer) at the time the cold mix is beingprepared instead of withholding the stabilizer until the mix temperatureis brought up to 160.F.

COOLING RATE COMPARISONS The increase in effectiveness of the coolingstep which follows from the substitution of the ester for the alginicsalt composition is illustrated by the results of the followingexperiments. In these tests, identical ice cream mixes containing 12%butter fat, serum solids and 14% sugar were treated with equalproportions of the two stabilizing agents. The weight of compositionadded was calculated on its sodium alginate content, the othercomponents being inert as regards stabilization. The alginic ester wasused as such, not as a composition.

In order to eliminate any possibility of error following fromdifferences in viscosity of the orig-' inal alginic acid used in thepreparation of the stabilizers, all were prepared from the same sampleof alginic acid, which was selected to have a 10W viscosity-producingfactor. The differences in viscosity noted below would have been muchgreater had a high viscosity acid been used as the starting material.

The pasteurizin'g procedure followed was such as permitted thecomposition to pass completely into solution. The mixes were heated to160 F. and the stabilizer added at that temperature. Afterpasteurization for one-half hour at 160 F. the mixes were homogenized at2500 pounds pres sure and immediately fed over a surface cooler, therebeing only an inappreciable intervening drop in temperature.

In the set of tests the results of which are shown in Table 1 the feedrate was maintained as nearly as possible uniform and equal, thedifference in effectiveness being indicated by differences intemperature of the mixes flowing from to maintain the uniform feed ratefor the mix stabilized with the composition, the cooled mix being soviscous that it stacked up in the trough and required that the feed bereduced. In each case the viscosity and temperature of the mix weretaken as it came off the cooler.

TABLE 1 Cooling tests at constant feed rate Vis. of Mix Temp. oil CoolerTest No 0013c of i e Algmate 9F Comp Ester Comp. Ester Per cent Cp. Cp.F. F.

In another'experiment the feed rates were so controlled as to bring twomixes off the cooler at the same temperature (40 F.) the variable beingthe time required to feed the test quantity (2 gallons) over the cooler.The mix stabilized with the alginic salt composition had a viscosity of640 cp. and the feeding time was 360 seconds. The mix stabilized withthe alginic ester had a viscosity of cp. and the feeding time was 324seconds, or 10 percent less than with the compo sition.

A reduction of ten percent in cooling time is a material advantage inthe every day operation of an ice cream plant; The cooling time would ofcourse be still further reduced if advantage were taken of thepossibility of pasteurizing mixes stabilized with the ester at a lowertemperature, for example F. instead of at F. As it is the practice topass the pasturized mix directly to the cooler, the mix pasteurized atthe lower temperature has less sensible heat to be withdrawn and thecooling time required to reach a desired temperature is reduced, as isthe amount of refrigeration required.' Mixes stabilized with the alginicsalt composition cannot be pasteurized at this lower temperature byreason of the incomplete solubilit of the composition.

EFFECT OF MIX ACIDI'IY ON SOLUBILITY The acidity of the mix has animportant efiect on the solubility of the alginic salt composition.Normal acidity, determined by titration with an alkali and expressed aslactic acid, is ordinarily about 0.20% for a mix containing 11% serumsolids and increases as the serum solids increase.

The normal acidity of condensed milk maybe I screens of the homogenizer.

h In order to ascertain the effect of varying degrees of acidity on thesolubilities of the ester and of the composition, samples of ice creammix were allowed to stand at room temperature for different periods oftime until they had developed acidities varying from 0.18% for fresh mixto 0.55% for aged mix. Each sample was then divided, each part beingtreated with the same quantity of the alginic salt composition or thealginic ester, thequantity added being 0.125%,by weight. The additionswere made at 160 F. as in the previous tests, the results as tosolubility being noted as set forth in Table 2 below:

These tests show a satisfactory solubility of the ester in eachinstance, regardless of the acidity of the mix. The solubility of theester in test No. 6, in which the developed acidity was 0.55%, was equalto that in test No. 3 in which the acidity was only 0.31%, and onlyslightly poorer than that in tests Nos. 1 and 2 in which the acidity wasnormal for a fresh mix. On the other hand, the alginic salt compositiongave poor solubility in test No. 3 and in the remainder of the tests, inwhich the acidity ranged from 0.43% to 0.55% the particles of alginicsalt merely swelled in the mix and settled to the bottom of thecontainer when agitation ceased.

EFFECTS OF AGING ON STABILIZED MIXES It is characteristic of mixesstabilized with a If it is preferred to freeze immediately-after coolingand batch freezing is practiced, delay may be avoided in the use of theester by adding a minute proportion of a powerful emulsifying agent,such as the polyoxyethylene derivatives of stearic acid described in thecopending application of Steiner & Miller, Serial No. 732,128, March 3,1947, or the similar derivatives of sorbitan oleates and stearatesdescribed in the copending application of Arnold B. Steiner, Serial No.691,667, filed August 19, 1946.

UNIFORMITY OF STABILIZATION Samples of the mixes used in the experimentsof Tables 1 and 3 were frozen after aging 12 hours in a six quart,counter type batch freezer to 100% overrun and were hardened in theusual manner. Pint cartons of the resultant ice creams were submitted toheat shock and shrinkage tests by holding the frozen samples for abouttwo weeks in an insulated cabinet in which the temperature fluctuatedbetween 5" and +12 Fahr.

The stored samples showed substantially no shrinkage nor ice crystalgrowth and all the ice creams were of good body and texture. The onlydistinction between ice creams stabilized with the composition and withthe ester was observed sodium alginate composition to develop their fullviscosity and their maximum whlppability immediately, during the coolingstep. It is characteristic of mixes stabilized with the alginic ester todevelop their full viscosity slowly and to attain maximum whippabilityonly after the lapse of several hours.

These widely divergent characteristics are illustrated by the results ofan experiment in which samples of the same fresh mix were stabilized at0.125% concentration with the alginic salt composition and the alginicester respectively. The mixes were held at F. for 96 hours and testedfor viscosity at 24 hour intervals, any error due to thixotropy beingavoided by passing the samples through a coarse screen before each test.The results are set forth in Table 3 below: 7

TABLE 3 Vz'scosities after aging Viscosity in Oentipoises As in theprevious tests, the composition and the ester were made from the samealginic acid and the quantity added was calculated on the sodiumalginate component of the composition, the ester being added as such.

Samples of the above mixes were frozen immediately after cooling andalso after aging for 24 hours. In the case of the mix stabilized withthe ester it was difficult to obtain 80% overrun on the fresh mix in abatch freezer, while the aged mix and both the fresh and the aged mixstabilized with the composition whipped to 100% overrun withoutdifliculty in both batch and continuous freezers.

when the amount of the stabilizer used exceeded the normal. For example,when the additionof stabilizer was increased from 0.125% to 0.150% theice cream stabilized with the composition had a heavier, chewier bodythan that stabilized with the ester. At a concentration of 0.125% theLIMITATIONS AS TO PROPERTIES OF THE ESTER I To obtain a whollysatisfactory ice cream stabilizer, certain limitations as to theproperties of the propylene glycol ester should 'be observed. The degreeof esterification has a marked effect on the value of the ester as astabilizer while the viscosity factor and the mesh size, though lesscritical, have considerable influence on the convenience with which theproduct may be used.

For the purpose of noting the effects of varying degree ofesterlfication, samples of the ester were prepared by acting on the samelow viscosity alginic acid with varying amounts of propylene oxide. Theresultant esters varied from 24% to 70% esterificatlon and were testedas to milk solubility, mix solubility, mix viscosity and temperature offcooler, at a uniform concentration of 0.150%. The results of these testsappear in the table below: TABLE 4 Variations in esterification Behaviorin Ice Cream Mix Pct Sol. in Milk Flow over Cooler Per cent F.

24 Poor Fair." Thlick, heavy, very 1,730 52 8 0w. 27 do. do do 1,280 5040 do. .-do Heavy, slow 440 y 48 47 Complete. G Thin, fast. 180 43 70.d0 do. do 43 1 Numerous insoluble particles floating on surface.

While all the above mixes made well stabilized ice creams, the excessiveviscosity and resultant the esters at equal concentration may be broughtabout by differences in degree of esterification. as above described, byvariations in the chain length of the original alginic acid, and byother causes. We classify as high viscosity such esters as show, inaqueous solution at 2% concentration, at 20 cent. and at pH 3.5 aviscosity over 3500 centipoises, and as low viscosity such esters asshow a viscosity of 1500 centipoises or less under the same conditions,all being over 40% esterifled.

Regardless of the cause, a high viscosity in aqueous solution retardsthe flow over the cooler, elevates the temperature of the cooled mix andlengthens the time required for freezing to a given overrun.

These effects are illustrated by the results of an experiment in whichsamples of the same mix were stabilized each with 0.125% of esters ofvarying viscosity, all being over 40% esterifled and of the sameparticle size, and the stabilized mixes were cooled and frozen. Theresults appear in the table below:

TABLE 5 tested as to solubility in milk at 145 F. with 20 minutesstirring. The low viscosity ester was completely and readily solubleunder these conditions while the medium and high viscosity esters wereincompletely soluble, gel-like particles floating on the surface of themix at the end of the stirring period. These higher viscosity estersbecome soluble at a somewhat higher temperature.

As ready solubility at a relatively low temperature, reduction oftemperature of the mix over the cooler, and acceleration of freezing,are all desirable qualities, we prefer to use an ester of moderate tolow viscosity, for example, not over 2500 centipoises in 2% aqueoussolution. The esters of higher viscosity, however, are functionalprovided the high viscosity is not due to insufficient esterification. VThe particle size to which the solid ester is reduced has, an importanteffect on its solubility. For example, a low viscosity ester sized topass through a 20 mesh standard screen dissolved only partially in anice cream mix during 30 minutes pasteurization at 160 F., while the sameester sized to pass through a 60 mesh screen dissolved completely underthe same conditions.

These differences are accentuated in mixes of developed acidity. In onetest at an acidity of 0.50% an 80 mesh ester dissolved completely, a 60mesh product dissolved somewhat less readily 8 while a 20 mesh estershowed numerous undissolved particles floating in the pasteurized mix.

For these reasons we prefer that the ester should be sized to passcompletely through a 40 mesh screen, though it is reserved that productsof coarser mesh are functional under favorable conditions.

The quantity of the ester required to produce proper stabilization ofthe frozen product will in no case exceed 0.250% of the weight of themix and in most cases will vary within the range from 0.075% to 0.150%by weight. Additions greater than the above maximum do not interferewith stabilization but have an undesirable effect on viscosity as wellas being wasteful.

It is desirable though by no means essential to blend the comminutedester with more or less an equal weight of an inert diluent such assugar or dextrin. Such diluents facilitate dispersion of the powderthrough the mix and to that extent improve solubility; they facilitateth weighing out of the small quantities required for an individualbatch, and they permit standardization of the stabilizing effect ofesters which vary in that respect by making a corresponding variation inthe extent of dilution. These agents function as diluents only, havingno stabilizing effect, and the phosphates or other buffer salts requiredin the alginic salt composition are not needed and should not be used.

A limitation to not less than 40% esterification means that not lessthan 40% of the carboxyl groups of the alginic acid are combined withthe propylene glycol radical, the remainder being either free orneutralized by a base which yields water-soluble alginates.

We claim as our invention:

1. The method of stabilizing an ice cream which consists in adding tothe ice cream mix, prior to freezing the same, a small but eifectivequantity of a propylene glycol ester of alginic acid, said acid beingnot less than 40% esterified and in the form of solid particles whichwill pass substantially completely through a 40 mesh standard screen.

2. The method of stabilizing an ice cream which consists in adding tothe ice cream mix, prior to freezing the same, a small but effectivequantity of a propylene glycol ester of alginic acid, said acid beingnot less than 40% esterified, said ester having a viscosity in aqueoussolution at 2% concentration and pH 3.5 not substantially exceeding 2500centipoises.

3. An ice cream stabilized by the presence of a small but effectivequantity of a propylene glycol ester of alginic acid, said acid beingnot less than 40% esterified.

4. An ice cream stabilized by the presence of a small but effectivequantity of a propylene glycol ester of alginic acid, said ester havinga viscosity in aqueous solution at 2% concentration and pH 3.5 notsubstantially exceeding 2500 centipoises, the acid of said ester beingnot less than 40% esterified.

- ARNOLD B. STEINEE.

GERALD D. SPERRY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,097,229 Lucas et al. Oct. 26,1937 2,426,125 Steiner Aug. 19, 1947

